Method for preparing metal aluminum hydrides



United States Patent 3,119,651 METHOD FOR PREPARENG METAL ALUMINUM HYDRIDES John C. Powers, Jr., 6 Franklin St, Marblehead, Mass. No Drawing. Filed Apr. 6, 1960, Ser. No. 20,249 17 Claims. (Cl. 23-14) This invention relates to a method for preparing metal aluminum hydrides having the formula M(A1H.;) where M is an alkali metal or alkaline earth metal and x is the valence of the metal. More particularly, the invention relates to a method for preparing sodium aluminum hydride.

The patent to H. I. Schlesinger and A. E. Finholt No. 2,567,972, dated September 18, 1951, describes a method for preparing a metal aluminum hydride having the above formula. This method comprises reacting a hydride of an alkaline metal or alkaline earth metal with an aluminum halide in an ether reaction medium. The reaction is illustrated by the equation:

Lithium aluminum hydride of high purity has been prepared in high yield commercially for several years by this method. However, the method has not been found satisfactory for the preparation of sodium aluminum hydride and other metal aluminum hydrides.

I have discovered -a method whereby sodium aluminum hydride and other alkali metal and alkaline earth metal aluminum hydrides having the formula M(AlH can be synthesized directly from the elements. In accordance with the invention an alkali metal, such as sodium, potassium or lithium, or an alkaline earth metal, such as calcium or magnesium, or the hydride of such alkali or alkaline earth metal, is heated at an elevated temperature in a confined reaction Zone with finely divided aluminum metal and a catalytic amount of a reaction promoter in an inert liquid carrier in the pressure of hydrogen under superatmospheric pressure while agitating the mixture until reaction between the aluminum, hydrogen and the alkali metal or alkaline earth metal or hydride thereof is complete. I have found a temperature between about 100 C. and 200 C. and a hydrogen pressure between about 2500 and 5000 p.s.i. to be suitable. A higher pressure may be used but is not necessary.

Suitable reaction promoters for use in the practice of the invention are amine boranes. I have found pyridine borane and the mono-, diand tri-lower alkyl amine boranes, such as mono-, di-and tri-methyl, ethyl, propyl, isopropyl, octyl and dodecyl amine boranes, etc. particularly suitable. The amount of such reaction promoter used may vary from about 0.1 to 25.0 percent or more by weight based upon the weight of alkali metal or alkaline earth metal initially in the reaction mixture.

Suitable inert liquid carriers are saturated liquid hydrocarbons, such as hexane, octane, ligroin and cyclohexiane; the lower alkyl ethers, such as dimethyl ether, diethyl ether, diisopropyl ether, and dibutyl ether; and ethers, such as tetrahydrofuran, dioxane or the dimethyl ether of ethylene glycol. Preferably, the liquid carrier should contain an amount of a solvent for the reaction promoter sufiicient to dissolve the same.

The invention is illustrated further by the following specific example.

3,119,651 Patented Jan. 28, 1964 8.1 grams of 30 mesh aluminum metal, 7 grams of sodium metal, one gram of dimethyl amine borane and 125 ml. of tetrahydrofuran were charged into a 250 ml. Magus-Dash reactor fitted with a magnetic agitator and suitable heating means. Hydrogen was introduced into the reactor under a pressure of 3000 p.s.i. The reaction mixture then was heated for 16 hours at a temperature of about 175 C. with continuous agitation. 11.4 grams of sodium aluminum hydride was isolated from the reaction mixture having a purity of 98 percent and representing a yield of percent.

I claim:

1. The method for preparing a metal aluminum hydride having the formula M (A111 where M is a metal selected from the group consisting of alkali metals and alkaline earth metals and x is the valence of the selected metal which comprises heating in a confined reaction zone a material selected from the group consisting of a alkali metals, alkaline earth metals and hydrides of such metals with finely divided aluminum metal and an amine borane selected from the group consisting of pyridine borane and lower alkyl amine boranes in amount from about 0.1 to 25 percent by weight based upon the weight of said selected material used in an inert liquid carrier at a temperature above about C. but below the decomposition temperature of the metal aluminum hydride in the presence of hydrogen under superatmospheric pressure above about 2500 p.s.i. while agitating the mixture until reaction between said selected material, aluminum and hydrogen is substantially complete.

2. The method as claimed by claim 1 wherein said selected material is sodium metal.

3. The method as claimed by claim 1 wherein said selected material is sodium hydride.

4. The method as claimed by claim 2 wherein said amine borane is a lower dialkyl amine borane.

5. The method as claimed by claim 2 wherein said 'amine borane is dimethyl amine borane.

6. The method as claimed by claim 2 wherein said liquid carrier contains a solvent for said amine borane in an amount sufiicient to dissolve the same.

7. The method as claimed by claim 2 wherein said elevated temperature is between 100 C. and 200 C. and said pressure is between about 2500 and 5000 p.s.i.

8. The method as claimed by claim 3 wherein said amine borane is a lower alkyl amine borane.

9. The method as claimed by claim 3 wherein said amine borane is dimethyl amine borane.

10. The method as claimed by claim 3 wherein said liquid carrier contains a solvent for said amine borane in an amount sufiicient to dissolve the same.

11. The me t hod as claimed by claim 3 wherein said elevated temperature is between 100 C. and 200 C. and said pressure is between about 2500 and 5000 p.s.i.

12. The method as claimed by claim 4 wherein said liquid carrier contains a solvent for said amine borane.

13. The method as claimed by claim 8 wherein said liquid carrier contains a solvent for said amine borane.

14. The method as claimed by claim 12 wherein said elevated temperature is between 100 C. and 200 C. and said pressure is between about 2500 and 5000* p.s.i.

15. The method as claimed by claim 13 wherein said elevated temperature is between 100 C. and 200 C. and said pressure is between about 2500 and 5000 p.s.i.

a 16. The method as claimed by claim 14 wherein said 2,729,540 Fisher Ian. 3, 1956 amine borane is dimethyl amine borane. 2,900,402 Johnson Aug. 18, 1959 17. The method as claimed by claim 15 wherein said 2,920,935 'Finholt Jan. 12, 1960 amine borane is dimethyl amine borane. 2,988,427 Jenkner et a1 June 13, 1961 5 2,992,248 Pearson July 11, 1961 Refelzrgfrirtrhe fit A0; 1115 patent OTHER REFERENCES ES NTS Germany printed application, 1,038,019, printed Sep- 2,372,671 Hansley Apr,3,1945 tembe,41958 

1. THE METHOD OF PREPARING A METAL ALUMINUM BYDRIDE HAVING THE FORMUAL M(ALH4)X WHERE M IS A METAL SELECTED FROM THE GROUP CONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS AND X IS THE VALENCE OF THE SELECTED METAL WHICH COMPRISES HEATING IN A CONFINED REACTION ZONE A MATERIAL SELECTED FROM THE GROUP CONSISTING OF A ALKALI METALS, ALKALINE EARTH METALS AND HYDRIDES OF SUCH METALS WITH FINELY DIVIDED ALUMINUM METAL AND AN AMINE BORANE SELECTED FROM THE GROUP CONSISTING OF PYRIDINE BORANE AND LOWER ALKYL AMINE BORANES IN AMOUNT FROM ABOUT 0.1 TO 25 PERCENT BY WEIGHT BASED UPON THE WEIGHT OF SAID SELECTED MATERIAL USED IN AN INERT LIQUID CARRIER AT A TEMPERATURE ABOVE ABOUT 100*C. BUT BELOW THE DECOMPOSITION TEMPERATURE OF THE METAL ALUMINUM HYDRIDE IN THE PRESENCE OF HYDROGEN UNDER SUPERATMOSPHERIC PRESSURE ABOVE ABOUT 2500 P.S.I. WHILE AGITATING THE MIXTURE UNTIL REACTION BETWEEN SAID SELECTED MATERIAL, ALUMINUM AND HYDROGEN IS SUBSTANTIALLY COMPLETE. 